Keyboards lend themselves as extension bases for other functions. For example, U.S. Pat. No. 5,841,424 describes a keyboard that has multiple extension bases with serial ports.
FIG. 1 shows an overview of a generic USB keyboard with additional extensions. Keyboard 100 contains a USB hub 110 with USB interface 105, which is connected through USB link 104 to a port 103 on the host computer system 101. USB hub 110 controls, in this example, a keyboard controller 131. The controller 131 has a keyboard matrix 132 and its own USB port 130, which connects to USB port 112 of hub 110. A card reader 120 is also present, with a media port 121. Card reader 120 has a port 113 that also connects to the USB hub 110 via USB port 111.
The approach shown in FIG. 1 results in a relatively expensive product. It requires at least three serial interface engines (SIEs), three processors or controllers (for each of the entities of the hub, the card controller, and the keyboard controller), and extra logic to handle general functions.
What is needed is an integrated, more cost-effective method that allows multiple, multi-pin devices to be connected via one USB line to a host computer, thus reducing the need for expensive multiple internal USB connections.